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TT: Tiefe Temperaturen
TT 25: Correlated Electrons - Low-dimensional Systems: Models
TT 25.5: Vortrag
Dienstag, 8. März 2005, 11:00–11:15, TU H2053
Effects of Frustration in The Auxiliary-Fermion Approach to The 2D Quantum Heisenberg Model — •Jan Brinckmann and Peter Wölfle — Institut für Theorie der Kondensierten Materie, Uni Karlsruhe, D-76128 Karlsruhe
Recently we studied the nearest-neighbor quantum-antiferromagnetic Heisenberg model for spin 1/2 on a two-dimensional square lattice [1]. A self-consistent approach based on the auxiliary-fermion representation of spin operators yields a correlation length ξ(T)∝exp(2πρS/T) as well as signatures of short-range order in the dynamical structure factor, in good agreement with the literature.
In the present work we study the effect of quantum fluctuations caused by an additional next-nearest-neighbor coupling J2 (J1-J2-model). In mean-field theory the order parameter is finite at the border η= J2/J1= 1/2 between the Néel and collinear ground states, corresponding to a finite stiffness ρS at T>0 . Within the self-consistent approach, however, we find that strong fluctuations drive ρS→ 0 at η= 1/2 . We also study the influence of the local Hilbert-space constraint on the auxiliary particles by comparing two variations of the approach: First the constraint is approximately replaced by a global one (as has been utilised in [1]), second the constraint is imposed exactly using a method proposed in [2].
[1] J. Brinckmann, P. Wölfle, Phys. Rev. B 70, in press (cond-mat/0405438)
[2] V. N. Popov, S. A. Fedotov, JETP 67, 535 (1988)